I don't think it is "illegal" but there is a US class action lawsuit.
It is not manufactured or installed anymore.
Suggest you call a licensed plumber to evaluate replacement. If you are selling your home, the value will be reduced due to it's presence.

ALL PERSONS THAT OWN, HAVE OWNED, LEASE, OR HAVE LEASED, AND ALL THOSE WHO HAVE OR MAY PURSUE CLAIMS THROUGH OR IN THE NAME OR RIGHT OF THEM, BUILDINGS, HOMES, RESIDENCES, OR ANY OTHER STRUCTURES IN THE UNITED STATES AND CANADA THAT CONTAIN, OR AT ANY TIME CONTAINED, KITEC PLUMBING SYSTEMS AND/OR COMPONENTS. YOUR LEGAL RIGHTS ARE AFFECTED WHETHER YOU ACT OR CHOOSE NOT TO ACT. PLEASE READ THIS WEBSITE CAREFULLY.

Homeowners whoseproperties are fitted with Kitec plumbing are being called on to claim theirpart of a settlement ina majorclass-action involving faulty water systems.Kitec plumbingwas originally billed as a more affordable and easier-to-install alternative tocopper piping. However, thefittings and pipes were found to be vulnerable to deterioration; metal withinthe plastic would come into contactwith another typeof metal at the joints, exacerbating corrosion.It is estimatedthat about 292,000 North Americans have Kitec plumbing in their buildings.Over the pastseven years, 4,412 North American property owners have applied for – andreceived – partial compensation after theirKitec plumbingfailed, leading to leaks and/or flooding. CBC News reports that thereare another 9,531 building owners inNorth America whohave Kitec plumbing and have yet to experience leaks, but who have filed aclaim.American andCanadian courts approved a $125 million settlement over the Kitec case on 2012,with 25% designated for legal fees.However, lessthan $3 million has been paid in claims, so far.Home inspectionexperts recommend that homeowners who discover that their house has been fittedwith Kitec should immediately inform their insurers.“On a homeinspection standpoint, it is a concern,” said AmeriSpec Inspection Servicesinspector Rob Iseppi. “Some of theinsurance companies are now not wanting to insure it, or wanting anotherinspection by a plumber typically.”Claims for thesettlement are due January 2020, CBC News reported, with claims frompeople who have yet to experience leaksfrom thedefective piping to be processed after the deadline.

https://www.cbc.ca/news/canada/nova-scotia/class-action-settlement-kitec-plumbing-1.4971290?fbclid=IwAR3CKanUpgKBqfWM04Pqv1qfCj2lDjt NbPYxfZ73267zhT9zMilfUE0j8P0There's$97M waiting for homeowners with Kitec plumbing. Why don't they claim it?Seven years after a $125-million class-actionsettlement over Kitec plumbing, less than $3 million has been paid out. One lawyerinvolved in the case is urging people with Kitec to file a claim. Lawyersays 'just a fraction' of eligible applicants have sought compensation

Kitec fixtures and pipes arethe subject of a $125-million class-action settlement, but few who have theplumbing in their homes have applied for compensation. (Robert Short/CBC)23 commentsThere is more than $97 millionwaiting to be claimed in aKitec class-action settlement, but it seems Canadians areeither unaware that money is available to pay to repair the plumbing or notinterested in making a claim."I suspect that notenough people know about the settlement and that is the primary reason,"said David Robins, a partner at Strosberg Sasso Sutts LLP, one of thefirms handling the class action.He said "just afraction" of eligible applicants have sought compensation.The $125-million settlementcovers North America and was approved by American and Canadian courts. Twenty percent was designated for legal fees, notices and other administration, leaving$100 million to pay claims for leaks and floods caused by Kitec fixtures andpipes.The settlement becameeffective on Jan. 10, 2012 but in the past seven years less than $3 million hasbeen paid in claims.Partial payments intentionally"very modest"It's estimated 292,000 NorthAmericans have the product in their homes. It's unknown how many of those homesare in Canada.It was widely used in theearly 2000s and late 1990s before it was recalled because both the fittings andpipes were prone to deterioration. Kitec, billed as a cheaper andeasy-to-install alternative to copper piping, was used primarily in hot waterbaseboard and in-floor heating systems. The product may also have other brandnames, including PlumbBetter, IPEX AQUA and WarmRite.